Each bar is a named model, and the length is how many days passed since the previous name was announced. The scale is linear. 916 days is the full width. GPT-6.1 Sol is the last bar: 7 days after Sol. Nothing has replaced it, so it has no bar after that.
The number on a row is days since the previous announcement, not days until retirement. GPT-1 is the start of the count, so it has no bar. Accent marks Astra, Sol, and GPT-6.1 Sol. Microsoft’s API stamp moves four earlier gaps by one day. The 19 and the 7 do not move.